Clopidogrel is a compound disclosed in U.S. Pat. No. 4,847,265 to be therapeutically useful as an inhibitor of platelet agglomeration.
Tablets containing clopidogrel as clopidogrel bisulfate are sold in the United States and elsewhere under the tradename Plavix™.
According to the labelling of Plavix™, each tablet contains 98 mg of clopidogrel bisulfate, which is the molar equivalent of 75 mg of clopidogrel. The tablets are made as cores which are then film coated. The cores comprise, in addition to the clopidogrel bisulfate, the following inactive ingredients: lactose, hydrogenated castor oil, microcrystalline cellulose, polyethylene glycol 6000 and pregelatinized starch. The weight of each tablet is about 240 mg.
Lactose and microcrystalline cellulose are ingredients that are commonly used as fillers and binders. Starch is commonly used as a disintegrant to cause the tablets to disintegrate in gastrointestinal fluid. Hydrogenated castor oil and polyethylene glycol are sometimes, although rarely, used as lubricants.
In the manufacture of tablets, it is generally necessary to include a lubricant in the mix of ingredients to prevent sticking of the compressed tablets to the punches, and also to prevent binding between the punches and the dies.
The most commonly used lubricant is magnesium stearate. U.S. Pat. No. 4,847,265, in examples 1 and 2, shows the use of magnesium stearate as the lubricant.
It is thus unusual that Plavix™ tablets do not contain magnesium stearate as the lubricant, but instead contain hydrogenated castor oil and polyethylene glycol as lubricants. Both of these ingredients have occasionally been used as lubricants, but they are not as effective as magnesium stearate, and their use in place of magnesium stearate must be expected to make it difficult to produce tablets at high speed without experiencing sticking to the punches or binding between the punches and dies. It appears that the reason that magnesium stearate is not used in Plavix™ tablets is that there is an interaction between clopidogrel bisulfate and magnesium stearate that causes degradation of the clopidogrel bisulfate, so that the stability of clopidogrel sulfate tablets which include magnesium stearate as lubricant is insufficient to enable sale of such tablets.
In light of this prior art, the object of the present invention is to provide stable clopidogrel hydrochloride tablets that contain a lubricant that is more effective than hydrogenated castor oil and polyethylene glycol 6000.